This research is directed toward understanding the regulatory mechanisms which govern the life cycle of Salmonella typhimurium temperate bacteriophage P22. These studies approach two central questions. What is the physical arrangement of genes on the P22 chromosome? What are the major regulatory signals which govern the P22 life cycle? The experiments proposed are directed toward three specific goals. 1) Prepare a physical-genetic map of the P22 chromosome. We are preparing a physical map in which the distance between any pair of restriction endonuclease cleavage sites will be proportional to the number of base pairs between the sites. When this physical map is complete, we will locate P22 genes with respect to the cleavage sites, resulting in a map in which the distances between genes on the map is proportional to physical distance between genes. 2) Determine the temporal sequence in which P22 genes function during the lytic cycle. Transcription of specific groups of P22 genes will be measured by hybridizing radioactive labeled RNA of infected cells with segments of P22 DNA carrying only a few genes. These segments will be obtained by restriction endonuclease cleavage of P22 DNA, or as P22 substitutions in lambda immP22 hybrid chromosomes. 3) Describe some mechanisms which regulate this temporal sequence of gene function. The action of major P22 regulatory genes will be defined in terms of differences in time or amount of transcription of specific groups of genes following infection by a regulatory mutant.